The invention generally relates to a combustion chamber arrangement for gas turbines. Preferably, it relates to one which includes a multiplicity of individual combustion chambers which open out in a common annular combustion chamber and are arranged in the shape of a circle. The invention also generally relates to a gas turbine having a combustion chamber arrangement which is constructed in accordance with the invention.
Gas turbines are in widespread use both in the field of power generation and as means for driving jet aircraft. In gas turbines, an air/fuel mixture is ignited in a combustion chamber, and the hot-gas stream resulting from the combustion is expanded into a turbine space, where the hot-gas stream comes into contact with an arrangement comprising guide vanes and turbine blades and sets the turbine blades arranged on a shaft and therefore the shaft itself in rotation. By way of example, a generator for generating power can now be operated with the aid of the rotary energy generated in this way.
Since the combustion of the air/fuel mixture results in high temperatures, which in modern, high-efficiency gas turbines may exceed temperatures of approximately 2000xc2x0 C., the turbine has to be cooled in the region of the combustion chamber and in subsequent regions, in terms of flow, in order to avoid overheating and therefore destruction of the turbine material.
Various attempted solutions are known both with regard to the structure of the combustion chamber and with regard to the required cooling. With regard to the structure of the combustion chamber, it is firstly known to provide a continuous annular combustion chamber in the form of a closed annular space which opens out into a first turbine space via an annular gap. In the annular combustion chamber, the air/fuel mixture is ignited, and an annular hot-gas stream which passes through the gap into the turbine space, where it drives the turbine blades, is formed. A problem with a solution of this type, in addition to undesirable, noisy fluctuations in the combustion, is the spatial limits imposed on the annular combustion chamber. Since the annular combustion chamber is accommodated entirely in the turbine housing, the volume of the combustion chamber cannot be increased or can only be increased with considerable structural outlay. However, such an increase in the volume is desirable in order for advanced combustion concepts to be implemented.
An alternative possible configuration for the combustion chamber consists in a multipart solution. A plurality of individual combustion chambers (known as can combustion chambers) are arranged in the form of a circle around an annular space into which the individual combustion chambers open out. The annular space serves as downstream annular combustion chamber, so that the actual combustion takes place in two parts. An air/fuel mixture is introduced into each of the individual combustion chambers and is ignited in the individual combustion chamber. The combustion then begins in the individual combustion chamber and continues via a transition region into the annular combustion chamber. In the annular combustion chamber, the gas streams from the individual combustion chamber are combined to form an annular gas stream which in turn opens out into a turbine space in order to drive the turbine blades.
A design of this type has the advantage that the combustion of the air/fuel mixture can be initiated in the individual combustion chambers and can therefore be carried out and controlled in a locally restricted manner. Consequently, it is possible to reduce or avoid undesirable oscillations in combustion which are associated with undesirable evolution of noise. It is also possible for the individual combustion chambers to project through the actual turbine housing, so that the former can be configured independently of the turbine design and can be expanded virtually as desired. For example, the larger combustion chamber volumes which are required for new and innovative combustion concepts can be made available without the basic design concept of the turbines, in particular the turbine mounting in the turbine housing, having to be completely revised.
Modern gas turbines are generally cooled by use of a fluid stream, usually a cooling-air stream. In this case, fundamentally two different concepts are employed. These are firstly what is known as impingement cooling, in which a cooling-fluid stream is guided onto the surface which is to be cooled, impinges on this surface and thus contributes to cooling. A second concept is convective cooling, in which a cooling fluid absorbs the heat which is generated and dissipates it by convection. A drawback of impingement cooling is that a pressure gradient is required in order to generated the gas stream which impinges on the surface which is to be cooled. Since in modern gas turbines some of the rotary energy of the turbine shaft obtained by the turbine is used in order to compress the air required to produce the air/fuel mixture, and this air is often also used as a cooling fluid, there is a loss of turbine efficiency if a pressure drop is additionally to be produced for cooling purposes. For optimum combustion, incoming air which is under high pressure is favorable, and consequently any pressure loss reduces the efficiency of the combustion. However, for effective impingement cooling a high pressure loss is necessary in order to pass a corresponding air jet onto the surface which is to be cooled. Furthermore, in the case of high-efficiency combustion, as can be achieved with combustion air which is under high pressure, relatively high temperatures are produced, which leads to increased cooling requirements and therefore, when impingement cooling is used, requires a higher pressure drop.
The situation is different in the case of convective cooling, in which a high pressure drop is not required in order to produce air jets. This type of cooling is advantageous with regard to turbine efficiency, but with this mode of cooling there are difficulties with regard to the cooling efficiency. For example, with convective cooling it is necessary for the cooling fluid, for example the incoming combustion air used for subsequent combustion, to be able to flow onto the individual regions which are to be cooled without being impeded, in order to generate a sufficient cooling effect. With many combustion chamber constructions, this cannot be achieved for design reasons, and consequently impingement cooling, which attenuates turbine efficiency, is often used.
An example of the use of impingement cooling in a combustion chamber arrangement with individual combustion chambers which open out into an annular space is given by U.S. Pat. No. 4,719,748. In the impingement cooling device described in this document, a transition region between the individual combustion chambers and a turbine stage of a gas turbine is surrounded by an impingement sleeve. An intermediate volume is formed between the impingement sleeve and the wall of the transition region, and the impingement sleeve has a multiplicity of openings. Cooling gases flow through these openings toward the wall of the transition piece, impinge on this wall and are thus responsible for cooling. A cooling concept of this type requires a high pressure drop between the outer side of the impingement sleeve and the interior volume, in order to allow jets of the cooling air to flow onto the surface of the wall of the transition region and provide the impingement for cooling at that location. As has been explained above, this pressure loss reduces the efficiency of the turbine.
An embodiment of the invention includes an object of further developing a combustion chamber arrangement in such a manner that it can be cooled using highly efficient convective cooling, with the use of impingement cooling being dispensed with as far as possible.
To achieve this object, an embodiment of the invention proposes that, in a combustion chamber arrangement, the annular combustion chamber, in a transition region to the individual combustion chambers, has a height which fluctuates periodically and is minimal in the region between adjacent individual combustion chambers.
Designing the annular combustion chamber in this manner allows a substantially more rectilinear flow guidance of the hot gas to be achieved, with a favorable transition from the individual combustion chambers into the downstream annular combustion chamber resulting. Moreover, designing the transition region between annular combustion chamber and individual combustion chambers in this way also allows favorable flow of a cooling fluid used for convective cooling onto the outer side.
To design the transition region between individual combustion chambers and annular combustion chamber in accordance with an embodiment of the invention, walls which delimit the annular combustion chamber are preferably designed in wavy form. In this case, the walls of the annular combustion chamber are arranged in such a way that openings of a maximum height and a minimum height alternately result in the transition region.
Further smoothing and gentle diversion of the hot-gas stream result if the annular combustion chamber, starting from the transition region which is formed with a periodically fluctuating height toward a turbine space connected downstream of the combustion chamber arrangement, in terms of flow, merges continuously into an annular space with a height which is uniform in the circumferential direction. In this way, the hot-gas streams which enter the annular combustion chamber from the individual combustion chambers in the transition region are distributed uniformly and are homogenized to form a single, annular gas stream. The continuous transition allows a pressure loss in the interior of the combustion chamber arrangement to be kept at a low level, which allows a high turbine efficiency to be achieved.
To be able to achieve targeted convection cooling, according to a further advantageous refinement of the invention, it is proposed that the housings of the combustion chamber arrangement be designed in the form of two shells. A gap space is preferably left between an inner shell and an outer shell and the shape of the outer shell is preferably matched to the shape of the inner shell in such a way that the distance between the two housing shells is substantially constant. With a two-shell structure of the housing of this type, it is possible to achieve good guidance of the cooling fluid used for convective cooling, the shape of inner shell and outer shell meaning that the cooling fluid which is guided in the gap space for cooling purposes reaches all the regions which are to be cooled uniformly, thus ensuring optimum cooling. On account of the shape of the inner shell and the outer shell of the housing, in the transition region between the annular combustion chamber and the individual combustion chambers, the gap space is transferred uniformly into individual gap spaces which surround the individual combustion chambers from a double ring which extends on both sides of the annular combustion chamber. This transfer takes place continuously and in gradual transitions, so that a gentle conversion of the cooling fluid flow without major pressure losses is possible. The avoidance of pressure losses at this point too contributes to the desired high turbine efficiency.
In a preferred configuration of the annular combustion chamber arrangement, finally, the individual combustion chambers are circular in cross section and are preferably designed in the form of a cylinder. A cross-sectional shape of the individual combustion chambers of this type on the one hand represents a suitable geometry for high-efficiency combustion, and on the other hand allows a smooth transition of the hot-gas flow from the individual combustion chambers formed in this way into the annular combustion chamber using the transition region described above.
Finally, an embodiment of the invention provides a novel gas turbine in which a combustion chamber arrangement as described above is used.